Time-of-flight sensing using continuous wave and coded modulation measurements

Abstract

A method for time-of-flight sensing is provided. The method includes for at least one pixel position performing at least one continuous wave measurement to obtain at least one first measurement value for the pixel position. Further, the method includes performing at least one coded modulation measurement to obtain at least one second measurement value for the pixel position. The method additionally includes determining an estimate of a distance value of the pixel position based on the at least one first measurement value and the at least one second measurement value using a mapping function.

What is claimed is: 
     
       1. A method for time-of-flight sensing of a scene, the method comprising for at least one pixel position:
 performing at least one continuous wave measurement to obtain at least one first measurement value for the pixel position; 
 performing at least one coded modulation measurement to obtain at least one second measurement value for the pixel position; and 
 determining an estimate of a distance value of the pixel position based on the at least one first measurement value and the at least one second measurement value, using a mapping function that maps an argument value derived from both a first value obtained from the first measurement value and a second value obtained from the second measurement value to an estimated distance value. 
 
     
     
       2. The method of  claim 1 , further comprising:
 determining whether the distance value is likely to be in a target distance range, wherein the estimate of the distance value is only determined if it is determined that the distance value is likely to be in the target distance range. 
 
     
     
       3. The method of  claim 2 , wherein determining whether the distance value is likely to be in the target distance range comprises:
 comparing a second value related to the at least one second measurement value to a threshold value defined for the target distance range; and 
 determining that the distance value for the pixel position is likely to be in the target distance range responsive to determining that the second value satisfies a predetermined condition with respect to the threshold value. 
 
     
     
       4. The method of  claim 2 , wherein determining whether the distance value is likely to be in the target distance range comprises:
 determining whether a first value related to the at least one first measurement value is within a first value range defined for a beginning of the target distance range or within a second value range defined for an end of the target distance range; 
 responsive to determining that the first value is within the first value range:
 comparing a second value related to the at least one second measurement value to a first threshold value defined for the target distance range; and 
 determining that the distance value for the pixel position is likely to be in the target distance range if the second value satisfies a predetermined condition with respect to the first threshold value; and 
 
 responsive to determining that the first value is within the second value range:
 comparing the second value to a second threshold value defined for the target distance range; and 
 determining that the distance value for the pixel position is likely to be in the target distance range if the second value satisfies a predetermined condition with respect to the second threshold value. 
 
 
     
     
       5. The method of  claim 2 , wherein determining whether the distance value is likely to be in the target distance range comprises:
 comparing a second value related to the at least one second measurement value to a first threshold value defined for the target distance range; and 
 responsive to determining that the second value satisfies a predetermined condition with respect to the first threshold value:
 scaling a first value related to the at least one first measurement value based on a scaling value to obtain a scaled first value; 
 comparing the scaled first value to the second value; and 
 responsive to determining that the scaled first value satisfies a predetermined condition with respect to the second value, comparing the first value to a second threshold value defined for the target distance range; and 
 determining that the distance value for the pixel position is likely to be in the target distance range, responsive to determining that the first value satisfies a predetermined condition with respect to the second threshold value. 
 
 
     
     
       6. The method of  claim 1 , wherein the method further comprises determining a ratio value based on a ratio of a first value related to the at least one first measurement value to a second value related to the at least one second measurement value, and wherein determining the estimate of the distance value of the pixel position comprises determining the estimate of the distance value based on the ratio value using the mapping function. 
     
     
       7. The method of  claim 1 , wherein one continuous wave measurement is performed to obtain one first measurement value for the pixel position, and wherein one coded modulation measurement is performed to obtain second measurement value for the pixel position. 
     
     
       8. The method of  claim 1 , wherein two continuous wave measurements are performed to obtain two first measurement values for the pixel position, and wherein two coded modulation measurements are performed to obtain two second measurement values for the pixel position. 
     
     
       9. The method of  claim 8 , wherein the method further comprises determining a ratio value based on a ratio of a first value related to the at least one first measurement value to a second value related to the at least one second measurement value, and wherein determining the estimate of the distance value of the pixel position comprises determining the estimate of the distance value based on the ratio value using the mapping function, and wherein the first value corresponds to a difference between the two first measurement values and the second value corresponds to a difference between the two second measurement values. 
     
     
       10. The method of  claim 1 , further comprising:
 determining an intensity of light received during the at least one continuous wave measurement based on the at least one first measurement value for the pixel position; 
 determining an intensity of light received during the at least one coded modulation measurement based on the at least one second measurement value for the pixel position; and 
 determining a greyscale value for a greyscale image based on the determined intensity of light received during the at least one continuous wave measurement and the determined intensity of light received during the at least one coded modulation measurement. 
 
     
     
       11. The method of  claim 10 , wherein at least one of the intensity of light received during the at least one continuous wave measurement and the intensity of light received during the at least one coded modulation measurement is further determined based on the estimate of the distance value. 
     
     
       12. The method of  claim 1 , wherein a respective absolute value of correlation functions of the at least one continuous wave measurement and the at least one coded modulation measurement is smaller than a threshold value for a predetermined distance. 
     
     
       13. The method of  claim 1 , wherein a ratio of correlation functions of the at least one continuous wave measurement and the at least one coded modulation measurement is strictly monotonic decreasing or strictly monotonic increasing in the target distance range. 
     
     
       14. The method of  claim 1 , wherein, if it is determined that the distance value for the pixel position is likely to be outside of the target distance range, the method comprises outputting an information indicating that an object in the scene at a position corresponding to the pixel position exhibits a distance not within the target distance range. 
     
     
       15. An apparatus for time-of-flight sensing of a scene, comprising:
 a time-of-flight sensor comprising a plurality of pixels, wherein the time-of-flight sensor is for at least one pixel position configured to:
 perform at least one continuous wave measurement to obtain at least one first measurement value for the pixel position; and 
 perform at least one coded modulation measurement to obtain at least one second measurement value for the pixel position; and 
 
 a processing circuit configured to determine an estimate of a distance value of the pixel position based on the at least one first measurement value and the at least one second measurement value using a mapping function that maps an argument value derived from both a first value obtained from the first measurement value and a second value obtained from the second measurement value to an estimated distance value.